Can a javascript check for jQuery and load it if not already present?

I'm just looking 开发者_开发问答for a simple javascript that can check to see if the jQuery library is already loaded and if not, loads it.

Thanks in advance if you have a solution.

if (typeof jQuery == 'undefined') {  
    // jQuery is not loaded => load it:
    var script = document.createElement('script');
    script.type = 'text/javascript';
    script.src = 'http://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js';
    document.getElementsByTagName('body')[0].appendChild(script);
}

Load script from Javascript by adding a <script> tag:

var fileref=document.createElement('script')
fileref.setAttribute("type","text/javascript")
fileref.setAttribute("src", filename)
document.getElementsByTagName("head")[0].appendChild(fileref)

Try this

if(typeof($) == 'undefined' || typeof(jQuery) == 'undefined'){//JQuery do not exist
    //Load the Jquery from your site or any CDN
}